The present invention relates to an intermediate sleeve which is adapted for use in flexographic, offset or gravure printing systems, and more particularly, to an intermediate sleeve including air channels and orifices therein which allow pressurized air to be supplied from a printing cylinder for the mounting and dismounting of printing sleeves.
In a typical flexographic printing process, a flexographic printing plate is attached to a printing cylinder, and as the cylinder rotates, the inked plate provides an image onto a substrate carried on an impression drum. It is conventional in the art to provide the printing plate in the form of a printing sleeve which is expandable by air pressure for mounting and demounting onto the print cylinder.
As is also known in the art, the diameter of the inner surface of an air-mounted printing sleeve must be slightly smaller than the diameter of the outer surface of the printing cylinder. However, depending on the type of print job performed, the sleeve may require a larger outer diameter while still maintaining a small inner diameter for fitting onto the printing cylinder. Multi-layer sleeves have been developed which provide a larger outer diameter and a small inner diameter. However, such multilayer sleeves are more expensive to manufacture than thin sleeves.
An alternative solution to the use of multi-layer sleeves has been the use of an intermediate or bridge sleeve, also referred to as a bridge mandrel, which can be used in combination with a thin printing sleeve, i.e., the thin sleeve is mounted on the intermediate sleeve with the use of pressurized air. Such intermediate sleeves must be able to deliver pressurized air to the outer surface of the sleeve to facilitate mounting and dismounting of the thin printing sleeve. One example of an intermediate sleeve is described in commonly-assigned U.S. Pat. No. 6,467,409, which teaches a bridge mandrel in the form of a cylindrically shaped tube including a channel extending around the circumference of the inner surface of the tube and including air holes or orifices extending radially outward from the channel to the outer surface of the tube. The channel and air holes permit pressurized air to be provided from the interior of the mandrel to its outer surface for mounting a printing sleeve to the mandrel. However, the design of the bridge mandrel restricts air conduction to those areas directly above the air exit holes.
Another known bridge sleeve manufactured under the designation Airo Light® is provided with an internal air conduction system which allows air to be delivered to predetermined outlet holes on the sleeve surface. The system comprises hoses which are embedded into the sleeve circumferentially and longitudinally and which are fixed by encapsulation with a cast polymer resin. Such hoses act as channels which receive pressurized air from a compressed air source and deliver it to the outlet holes. However, the use of such embedded hoses requires a greater minimum wall thickness for the sleeve. In addition, it is not possible to provide such longitudinal hoses in some types of intermediate sleeves.
Accordingly, there is still a need in the art for an improved intermediate sleeve for use in flexographic printing applications which facilitates the mounting of printing sleeves with the use of pressurized air but which does not suffer from the drawbacks of prior sleeves.